Projectors are generally devices that integrate light sources, optics systems, electronics, and displays for front- or rear-projecting images from computers or video devices. Typical projectors include spatial light modulators (SLM's) to modulate light spatially, so that images are projected onto screens for viewing. Light is transmitted to an SLM, which processes the light so that the desired image pixel is projected onto a screen. SLM's may be reflective in nature. Light is reflected off an SLM, which modifies the light in accordance with the image to be projected onto the screen. The archetypical example of this type of SLM is the digital micromirror device (DMD), which is a kind of micro-electromechanical (MEM) device. Projectors using DMD's project bright images, because the light does not have to transmit through the reflective SLM's.
In general, a projector refreshes its pixels with new data based on a refresh rate, or in every display period of
      1          refresh      ⁢                          ⁢      rate        .DMD's, however, are binary optical display elements, meaning that they either reflect light, or do not reflect light, and thus are not receptive to pixels having color depths greater than one bit. For a DMD to project a pixel having an intensity value of more than one bit in color depth, the display period is usually divided into a number of intervals, with each interval usually equal to or less than
            display      ⁢                          ⁢      period                      2                  color          ⁢                                          ⁢          depth          ⁢                                          ⁢          in          ⁢                                          ⁢          bits                    -      1        .In each interval the DMD is loaded with one of the bits of the intensity value of the pixel, so that it reflects light or does not reflect light in accordance with this bit. Each bit is loaded into the DMD a number of times based on its significance relative to the other bits of the pixel's intensity value.
The projector therefore typically refreshes each of its DMD's every interval of every display period. Each of these intervals is usually specified as no greater than
      1                  refresh        ⁢                                  ⁢        rate        ×                  (                                    2                              color                ⁢                                                                  ⁢                depth                ⁢                                                                  ⁢                in                ⁢                                                                  ⁢                bits                                      -            1                    )                    ⁢                            .For a projector having a color depth of eight bits and a refresh rate of sixty hertz (Hz), this means that the projector refreshes each DMD at intervals no longer than about sixty-five microseconds (μs). However, controlling all the DMD's in a projector in this manner can be difficult, especially for projectors with large resolutions and high refresh rates.